This invention generally relates to waste material confinement areas. More specifically, the present invention relates to covers for use in conjunction with such waste material confinement areas. The invention further relates to methods by which to use and produce such covers.
Waste material confinement areas, such as slurry tanks, ponds, concrete cells and waste lagoons are widely used in the treatment of organic waste, including human, animal, and food processing waste. Waste lagoons are especially economically attractive to livestock producers, such as confinement swine producers. However, odors generated from waste material confinement areas, particularly waste lagoons employed in livestock production, must be significantly reduced in order to meet environmental challenges and to avoid exposing the general public to malodorous fumes. Aerobic and anaerobic microorganisms are commonly used to decompose the materials comprising the organic waste. Unfortunately, gases generated by the microorganisms during the decomposition process can be malodorous.
Treatment processes employing anaerobic microorganisms are the most common. Anaerobic microorganisms naturally develop within the depths of waste material confinement areas, due to the lack of available oxygen. Regrettably, anaerobic microorganisms generate numerous malodorous gases during the decomposition process. These off-gases bubble up through the waste liquid and are problematic if allowed to enter the atmosphere.
The familiar smell of ammonia and the xe2x80x9crotten eggxe2x80x9d odor of hydrogen sulfide gas are typical of the odors produced during anaerobic decomposition. The metabolism of animal waste within a lagoon typically produces methane gas, carbon dioxide in solution and as a gas, hydrogen sulfide in solution and as a gas, and various volatile organic compounds. In fact, nearly two hundred odorous gases have been documented as a result of manure, rendered or processed animal waste and carcass decomposition, including volatile organic compounds such as para-cresol, phenol, indole and satol, and reduced sulfur gases. Several of the gases produced by anaerobic decomposition are especially malodorous, particularly volatile fatty acids.
Off-gases from anaerobic lagoons can pose other problems, as well. For example, ammonia emissions from anaerobic waste lagoons may contribute to acid rain. Methane emissions from anaerobic lagoons may contribute to global warming.
To capture noxious off-gases, anaerobic waste treatment processes generally employ an impermeable cover to encapsulate waste lagoon surfaces and capture the off-gases as they are released. The cover is typically formed from a polymeric film, such as a polyethylene membrane, suspended above the slurry. Gases trapped under the impermeable cover are subsequently removed by gas collection pipes, weighted sunken troughs, sump pumps, and the like. Such gas collection systems are described in U.S. Pat. No. 5,562,759. However, such covers and gas collection systems are expensive, require substantial support equipment, require time consuming and costly maintenance, are vulnerable to puncture, weather, vandalism, fatigue, and deterioration.
In contrast, wastewater treatment processes employing aerobic microorganisms do not utilize such impermeable membranes. In fact, rather than producing malodorous off-gases, aerobic microorganisms convert waste into innocuous compounds, such as carbon dioxide or nitrites. Further, aerobic microorganisms can degrade malodorous off-gases, such as the volatile fatty acids produced during anaerobic treatments. The aerobic bacteria transform the animal waste into a chemically stable material, reducing both pathogens and odor. Some types of aerobic microorganisms xe2x80x9cdigestxe2x80x9d or oxidize carbohydrates to carbon dioxide and water. Other strains feed on organic substances and convert nitrogen compounds to ammonium. Still others oxidize ammonium salts to nitrites and nitrites into nitrates in a process referred to as xe2x80x9cnitrification.xe2x80x9d
The aerobic microorganisms may be cultured on substrates submerged within the waste lagoon. However, aerobic microorganisms require oxygen to survive. Therefore, conventional aerobic processes used to treat liquid sludge must mechanically inject air into the waste water, which consumes energy, is costly, and requires maintenance. Further, such aerobic treatments do not totally eliminate the emission of gases having a foul odor, and present technology does not offer any effective odor control for this type digestive system. Numerous patents are directed to waste water treatment systems employing submerged aerobic microorganisms, including U.S. Pat. Nos. 4,165,281; 5,228,998; 6,022,476; 5,232,586; 5,861,095; 5,496,292; 5,580,770; 5,962,309; and 5,980,738.
In addition to submerged aerobic systems, aerobic microorganisms can also be used to treat noxious gas streams. For example, aerobic microorganisms can be grown on media which is either suspended within a closed vessel or floating on the surface of the waste slurry. The noxious gases are then treated as they diffuse though the suspended or floating media, commonly referred to as a xe2x80x9cbio-filter.xe2x80x9d Exemplary media employed to date includes floating organic matter, such as compost or peat moss, as well as synthetic materials for use in closed vessels.
However, aerobic gas scrubbing systems require a delicate balance of environmental conditions for the continued support of aerobic microorganisms. As noted above, aerobic microorganisms require air to survive. Therefore, once the host media becomes submerged, the function of the aerobic microorganism is terminated in the absence of mechanically introduced oxygen. However aerobic microorganisms can not survive in the total absence of water. Therefore, the bio-filter must be kept moist. Floating organic matter, lacking both sufficient buoyancy and structural integrity, is unstable and short lived as an aerobic bio-filtration substrate due to submersion. Aerobic filtration media suspended within vessels are problematic also, in that such systems require the mechanical introduction of moisture, such as by the use of spray nozzles and the like. Bio-filters employed to scrub gases within a reaction vessel are described in several patents, including U.S. Pat. Nos. 5,480,538; 6,069,003; and 5,714,379. Further, in vessel-type biofilters, the offensive gases must be collected first and then passed through the media. The existing technology and high cost of implementation limits the effectiveness to relatively small, confined areas and is presently too expensive for a majority of applications.
The present invention provides cost effective, sound waste treatment systems for a wide variety of waste material confinement areas, such as waste lagoons. The waste treatment systems generally include an anaerobic waste material confinement area and a waste material confinement area cover. The waste material confinement area covers of the present invention treat the off-gases produced by the anaerobic microorganisms within the depths of the waste lagoon, thereby eliminating the noxious odors commonly associated with such anaerobic decomposition. The waste material confinement area covers of the present invention are easily installed, highly buoyant, and structurally sound. The waste material confinement area covers are generally formed from two or more floatation panels joined by a fabric layer.
The floatation panels generally include a plurality of polymeric foam particles arranged in a piled laminate structure. At least a portion of the foam particles exhibit a surface energy differential in comparison to water sufficient to wick an adequate amount of water onto the foam particles to collectively sustain a biofilm supported by the floatation panel. At least a portion of the polymeric foam particles within the piled laminate structure are further bonded to at least one adjoining foam particle positioned either above or below the foam particle.
The piled laminate structure generally defines a first face and an opposing second face, the first face contacting an aqueous waste slurry at or near its surface. At least a portion of the foam particles further exhibit sufficient buoyancy to collectively float the floatation panel. The foam particles are arranged within the piled laminate structure so as to define interstices between at least a portion of the foam particles. The interstices are of sufficient size and quantity to allow gases and rainwater to flow through the piled laminate structure.
The polymeric foam particles within the floatation panels can be formed from one or more polymers selected from polyolefin, polyvinyl acetate and polyurethane. In advantageous embodiments, the polymeric foam particles are formed from either polyethylene, polypropylene or a mixture thereof. The polymeric foam particles generally range in diameter from about 0.5 to 2.0 inches. The polymeric foam particles can be bonded by any means, including thermal bonding, needlepunching, stitching and chemically binding. Advantageously, the polymeric foam particles are thermally bonded. In an alternative embodiment, the polymeric foam particles are needlepunched. In a further alternative embodiment, the polymeric foam particles are bonded by chemically binding.
Floatation panels of the present invention generally range in thickness from about 0.5 to about 2.0 inches. The instant floatation panels further typically exhibit a density ranging from about 1.5 to about 4.0 lb/ft3. In advantageous embodiments, the floatation panel can further include a fabric layer bonded to at least a portion of its first face. In beneficial aspects of that embodiment, the fabric layer bonded to the first face can be a nonwoven fabric.
As noted above, to form the waste material confinement area covers of the present invention, two or more floatation panels are joined using a fabric layer. The fabric layer may cover at least a portion of the second face of the floatation panel. In beneficial aspects, the fabric is formed from a fiber mixture including a first portion of fibers having a denier ranging from about 15 to 45 and a second portion of fibers having a denier ranging from about 3 to 10 denier. The fabric may be formed from numerous materials, including polyester, nylon, glass fiber, acrylic, flax, and polyolefin, including polypropylene and polyethylene, and mixtures thereof. In advantageous embodiment, the fabric is formed from polyester or acrylic fiber or a mixture thereof. The fabric may have any construction. In one aspect of the invention, the fabric layer is a nonwoven fabric. The fabric layer further generally exhibits a fabric weight ranging from about 14 oz/yd2 to 35 oz/yd2.
In beneficial aspects of the invention, the fabric layer can further comprise an entrapped adsorbent material. Exemplary adsorbent materials can be selected from zeolite, peat moss, activated carbon, and mixtures thereof. In one beneficial embodiment, the adsorbent material is zeolite. The adsorbent material may advantageously be present within the fabric in amounts ranging from about 0.5 to 10 g/m2.
In beneficial embodiments, the waste material confinement area covers of the present invention exhibit a buoyancy ranging from about 0.5 to 6 lb/ft2. Waste lagoon covers in accordance with the invention are further capable of decreasing ammonia emissions from a waste lagoon by a minimum of about 44%.
The invention further includes waste treatment systems including the beneficial waste material confinement area covers of the present invention. The waste treatment systems generally include a waste material confinement area containing water and organic waste and further supporting anaerobic microorganisms below the surface of the water and a waste material confinement area cover spanning the surface of the waste material confinement area. The waste treatment system can further include an anchor to secure the waste material confinement area cover around the perimeter of the waste material confinement area.
The present invention also encompasses methods of waste water treatment, which generally include supplying organic waste to a waste material confinement area; covering the surface of a waste material confinement area with a waste material confinement area cover of the present invention; providing an anchor around the perimeter of the waste material confinement area; and securing the waste material confinement area cover with the anchor. The waste water treatment methods of the present invention generally involve anaerobically digesting organic waste within the depths of a waste material confinement area and scrubbing the off-gases emitted during anaerobic digestion by diffusing them through a floatation panel prior to emitting the scrubbed gas stream into the atmosphere. In an alternative embodiment, the scrubbed gas stream may be passed through adsorbent filtration media prior to emitting the scrubbed gases into the atmosphere. In beneficial aspects of that embodiment, the adsorbent filtration media includes a layer of fabric containing entrapped adsorbent material.
The waste material confinement area covers, floatation panels and methods of the present invention can be used in a variety of waste treatment applications. Benefits of the present invention include a reduction in off-gas emissions from anaerobic waste lagoons. The present invention further provides reliable, durable, cost-effective waste treatment processes.
Further understanding of the methods and systems of the invention will be understood with reference to the brief description of the drawings and detailed description that follows herein.